Add an affix behavior to an element, by keeping it sticky between 2 elements.

sticky.js

;(function($) {
    $.fn.extend({
        stickyWidget: function(options) {

            // Exit if there are no elements to avoid errors:
            if (this.length === 0) {
                return this;
            }

            var settings = $.extend({
                header: '',         // The page header or any element that the sticky module should be affixed
                footer: '',         // The page footer or any element that the sticky module should stop when it hits
                minWidth: 980,      // The minimum width to enable sticky - usually the width of the content area
                threshold: 60,      // An extra buffer added to the height when determining whether or not to enable
                bufferTop: 0,       // Distance from top of page element should stick (added to element bottom margin)
                bufferBottom: 0     // Distance from footer to stop (added to element bottom margin)
            }, options);

            var sticky = {
                el: $(this),
                stickyLeft: 0,
                stickyTop: 0,
                stickyHeight: 0,
                win: $(window),
                header: false,
                footer: false,
                headerHasChanged: null,
                threshold: settings.bufferTop + settings.threshold + settings.bufferBottom
            };

            // Orginal positioning
            var orig = {
                mar: $(this).css('margin-left'),
                left: $(this).css('left'),
                top: $(this).css('top'),
                pos: $(this).css('position')
            }
            var timer;
            var stickyEnabled = true;

            cacheElements();

            return this.each(function() {
                buildSticky();
            });

            function buildSticky() {
                sticky.win.bind({
                    load: setupSticky,
                    sticky: setupSticky,
                    scroll: function () {
                        if (sticky.header.length) {
                            if (sticky.header.height() <= 158) { // yeah, magic static value 
                                if (sticky.headerHasChanged == null || sticky.headerHasChanged == 0) {
                                    setupSticky();
                                    calculateLimits();
                                    sticky.headerHasChanged = 1;
                                }
                                stick();
                            } else {
                                if (sticky.headerHasChanged == null || sticky.headerHasChanged == 1) {
                                    setupSticky();
                                    calculateLimits();
                                    sticky.headerHasChanged = 0;
                                }
                            }
                        } else {
                            stick();
                        }
                    },
                    resize: function() {
                        clearTimeout(timer);
                        timer = window.setTimeout(enableSticky, 200);
                    }
                });
            }

            function setupSticky() {
                console.log("setupsticky!");
                var mid = sticky.win.width() / 2;
                var widgetLeft = sticky.el.offset().left;
                sticky.stickyWidth = sticky.el.width();
                sticky.stickyLeft = widgetLeft - parseInt(mid, 10);
                sticky.stickyTop = sticky.el.offset().top;
                sticky.stickyHeight = sticky.el.outerHeight(true);
                enableSticky();
            }

            // Caches elements into jquery objects
            function cacheElements() {
                if (settings.header !== '' && $(settings.header).length !== 0) {
                    sticky.header = $(settings.header);
                }

                if(settings.footer !== '' && $(settings.footer).length !== 0) {
                    sticky.footer = $(settings.footer);
                }
            }

            // Only enable the sticky module if it's not going to break anything
            function enableSticky() {
                var ft = sticky.footer ? sticky.footer.offset().top : $(document).height();
                var track = (ft - sticky.threshold) >= (sticky.stickyHeight + sticky.stickyTop) &&
                            // do not check whether sticky content is taller than window height
                            //sticky.stickyHeight < sticky.win.height() &&
                            sticky.win.width() >= settings.minWidth &&
                            'ontouchstart' in window === false;

                if( track ) {
                    stickyEnabled = true;
                } else {
                    stickyEnabled = false;
                }
                calculateLimits();
                stick();
            }

            //  Calcualtes the limits top and bottom limits for the sidebar
            function calculateLimits() {
                sticky.stickyStart = sticky.stickyTop - settings.bufferTop;
                if(sticky.footer) {
                    sticky.stickyStop = sticky.footer.offset().top - sticky.stickyHeight - settings.bufferTop - settings.bufferBottom;
                }

            }

            // Sets widget to fixed position
            function setFixedWidget() {
                sticky.el.css({
                    position: 'fixed',
                    top: settings.bufferTop,
                    left: '50%',
                    marginLeft: sticky.stickyLeft,
                    width: sticky.stickyWidth + "px"
                });
            }

            // sets widget to a static positioned element
            function setStaticWidget() {
                sticky.el.removeAttr("style");
            }

            // initiated to stop the widget from intersecting the footer
            function setLockedWidget(diff) {
                sticky.el.css({
                    top: diff
                });
            }

            //determines whether sidebar should stick and applies appropriate settings to make it stick
            function stick() {
                var windowTop = sticky.win.scrollTop();
                var hitBreakPoint = stickyEnabled && sticky.stickyStart < windowTop;

                if (hitBreakPoint) {
                    setFixedWidget();
                } else {
                    setStaticWidget();
                }
                if (sticky.footer && sticky.stickyStop < windowTop) {
                    var diff = sticky.stickyStop - windowTop + settings.bufferTop;
                    setLockedWidget(diff);
                }
            }

        }
    });
})(jQuery);